Multi-Threshold Complementary Metal Oxide Semiconductor (MTCMOS) technology is being widely used for low power integrated circuit devices. In particular, it is known that power dissipation of an integrated circuit device may be reduced by reducing the power supply voltage thereof. Unfortunately, a reduction in power supply voltage may reduce the speed of the transistors of the device. Accordingly, it is known to reduce the threshold voltage (Vth) of the transistors to at least partially overcome this speed reduction. Unfortunately, a reduction in threshold voltage may increase the leakage or standby current of the transistors when they are in the “off” state, which may thereby increase power consumption when the device is in a standby state.
MTCMOS technology can overcome this potential increase in standby current by utilizing low threshold voltage transistors for logic operations of the device and by supplying power supply and/or ground voltages to the logic gates through transistors which have a high threshold voltage. When the high threshold voltage transistors are turned on to supply the power supply voltages to the logic gates, the low threshold voltage transistors can be operated at high speed because of their low threshold voltages. However, in standby mode, the high threshold voltage transistors may be turned off to thereby cut off the low voltage threshold transistors from their power supply voltages and thereby reduce or eliminate leakage current through the low threshold voltage transistors.
In some embodiments, MTCMOS devices have a configuration in which a MOS switch with a comparatively high threshold voltage is connected in series between a power supply and a logic circuit. It will be understood by those having skill in the art that as used herein, the term “MOS” refers to any insulated gate field effect transistor, the gate of which comprises metal and/or nonmetal (such as polysilicon) and the insulator of which comprises oxide and/or other insulators (such as high dielectric constant insulators).
MTCMOS technology can reduce or minimize the power consumption of a system by turning on the MOS switch to supply power to the logic circuit in an active mode and turning it off to interrupt the power to the logic circuit in a sleep mode. Thus, this technology may be used for reducing power consumption of a circuit used in a system in which the sleep mode is longer than the active mode.
However, if a transition when the power is interrupted is not provided properly, a virtual ground voltage level of the MTCMOS circuit may float during the sleep mode, and data stored in a latch circuit or flip-flop circuit connected to the MTCMOS circuit may be lost. Therefore, in order to properly operate the MTCMOS circuit, a flip-flop circuit for storing data in the sleep mode and a control circuit for controlling the MTCMOS device may be provided.